Following versions R8/9/10, R11 technology is further proposed for a Long Term Evolution (LTE) system. Some R8 products become commercially available gradually. Further product planning is required for R9 and R10.
Added with R10 on the basis of R8 and R9 are many new features, such as a pilot feature like a Demodulation Reference Signal (DMRS) and a Channel State Information Reference Signal (CSI-RS), as well as a transmission and feedback feature such as 8-antenna supporting. In particular, with enhanced Inter-Cell Interference Cancelling (eICIC) technology, inter-point interference avoidance is further considered on the basis of R8/9 ICIC. In a solution for inter-point interference in an initial stage of R10, mainly considered is point interference avoidance in a homogeneous network, with a mainstream being eICIC and Coordinated Multi-point (CoMP) technology. By name, with CoMP, multiple nodes are coordinated to send data to one or more UEs using the same or different time-frequency resources, which may reduce inter-point interference, increase point-edge throughput, and expand point coverage. In later discussion more scenarios introduced by a heterogeneous network are considered. Due to complexity of CoMP and limited time for R10 discussion, it is decided in the end to introduce no more CoMP standardization in R10. Rather, a CoMP demand may be taken into account in CSI-RS design. Therefore, CoMP is not discussed any further after the 60 bis conference.
In an initial Study Item of R11 discussion, unified assessment architecture is determined mainly via CoMP transmission technology and scenario planning. It is proved by two-stage CoMP assessment that a notable performance gain may be obtained with CoMP. A recent CoMP SI concludes that further study has to be done on Joint Transmission (JT), Dynamic Point Selection (DPS), Coordinated Scheduling (CS), Coordinated Beamforming (CB) in CoMP.
Before the study, one has to first ponder a difference in CoMP with R8/9/10, including that in measuring and reporting multi-node Channel State Information (CSI) by a UE, meeting different demands of CoMP transmission technology, and CoMP measuring set notification by CoMP control signaling. A solution for multi-node CSI measuring and reporting by a UE via CoMP is of a top priority. According to discussion at present, CoMP feedback mainly may include periodic feedback and aperiodic feedback, as well as aggregated CSI feedback and non-aggregated CSI feedback. With the so-called aggregated CSI feedback, CSI of multiple nodes is aggregated into that of one node for global feedback. For example, a measuring set contains two nodes, CSI of a node 1 being H1, and CSI of a node 2 being H2. A UE aggregates channels of both nodes into a greater set of CSI H=[H1; H2] before performing measurement-related computation and feedback. Mon-aggregated CSI feedback may further include separate single-point feedback and separate single-point feedback plus inter-point correction information. With the so-called separate single-point feedback, measurement-related computation and feedback is performed separately in accordance with CSI of each node. With the so-called separate single-point feedback plus inter-point correction information, measurement-related computation is performed separately in accordance with CSI of each node, and inter-node phase and/or amplitude information is computed before feedback is performed. Aggregated CSI includes feedback of an aggregated Channel Quality Indicator (CQI). An aggregated CQI fed back by a UE side is measured according to one or more sets of CSI-RS configuring information. The UE may find a time-frequency location corresponding to a CSI-RS using multiple sets of CSI-RS configuring information, perform measurement to obtain precoding weight information, and perform computation using interference information obtained by another pilot. Here, the UE is supposed to receive data sent by nodes corresponding to one or more sets of CSI-RS configuring information to obtain CQI in joint sending performed by the nodes. An aggregated CQI may correspond to aggregated measurement according to one or more sets of CSI-RS configuring information. For example, a measuring set may contain 3 sets of CSI-RS configuring information, in which case there are a total of 7 choices, 3 in aggregation of one set of CSI-RS configuring information, 3 in aggregation of two sets of CSI-RS configuring information, and 1 in aggregation of one set of CSI-RS configuring information. Therefore, there are many choices instead of one for aggregated CQI.
As a conventional R8/R9/R10 user only has to feed back serving point CSI, for both periodic feedback and aperiodic feedback, only single-point capacity has to be considered on the same carrier. In particular, it is enough to have single-point feedback optimized for a Physical Uplink Control Channel (PUCCH). At present, given coding and a number of Hybrid Adaptive Request Retransmission (HARQ) bits, a UE supports at most 11-bit CSI feedback in a PUCCH uplink subframe. The 11 bits may consist at most of a 4-bit Precoding Matrix Indicator (PMI) and 7-bit CQI of two codewords (given inter-codeword differential CQI feedback). With CoMP, multi-point CSI feedback has to be taken into account, which requires N*11-bit PUCCH capacity, which goes beyond current PUCCH capacity. Therefore, there has to be a sound feedback solution for inadequate PUCCH capacity. One may easily come up with feedback signaling compression. However, high CSI accuracy may be required for CoMP, especially for JT and even for JT-MU. Performance loss due to compression may lead to a lowered CoMP performance gain. Another consideration may be to increase PUCCH capacity by re-designing a PUCCH feedback format, which sure requires more standardization efforts. Given that requirement for CSI feedback differ with different CoMP modes and that adaptive switching between different modes may have to be ensured, such feedback design may get even more complicated. Therefore, it is discussed to introduce inter-node information that may ensure flexible coordinated transmission mode switching and/or introduce the concept of an aggregated CQI. it is discussed in a recent conference that similar performance may be obtained by an aggregated CQI and by inter-node information+aggregated CQI, in which case no comparison is made for introducing additional inter-node information feedback. The discussion over whether to introduce inter-node information feedback continues at the conference. However, with either solution introducing the concept of an aggregated CQI is considered. The concept is to feed back CQI produced by multi-node aggregation. A combination of an arbitrary number of nodes of all nodes in a measuring set may be aggregated. For example, for a measuring set containing six nodes, there are 63 possible combinations. Given an upper limit to the number of aggregated nodes, there may be 41 possible combinations. In case that a UE feeds back multiple aggregated CQIs of various cases once or by multiple subframes, an agreement has to be reached between a base station side and the UE side before the base station side can learn to receive the aggregated CQI feedback and learn the nodes in the combination fed back by the UE.
For R10 the feedback mainly may include periodic feedback and aperiodic feedback.
Aperiodic feedback has to be triggered by uplink authorization or random access authorization control signaling. Table 1 shows aperiodic feedback modes.
TABLE 1PMI Feedback TypeNo PMISingle PMIMultiple PMIPUSCHWidebandMode 1-2CQI(wideband CQI)FeedbackUE SelectedMode 2-0Mode 2-2Type(subband CQI)Higher Layer-Mode 3-0Mode 3-1configured(subband CQI)
An aperiodic reporting mode is configured to the terminal side by higher-layer signaling cqi-ReportModeAperiodic.
A Rank Indicator RI has to be fed back only when a base station side configures a terminal side to adopt transmission modes 3, 4, 8 and 9 with a PMI/RI feedback configuration. For a wideband feedback mode 1-2, a terminal side has to feed back multiple subband PMIs and a wideband CQI computed based on the multiple subband PMIs. A the mode 3-0 and a the mode 3-1 are for a higher-layer configured subband CQI. For the mode 3-0 a terminal side has to feed back a wideband CQI and multiple subband CQIs, both the wideband CQI and the subband CQIs being computed based on a codeword. For a transmission mode 3, different RIs have to be taken into account in CQI computation. For a transmission mode other than the mode 3, RI=1 is assumed in CQI computation. For a mode 3-1, a terminal side has to feed back a wideband PMI, and then compute and feed back a wideband CQI and multiple subband CQIs respectively according to the wideband PMI fed back. For transmission modes 4, 8, and 9, the CQI computation has to be based on the value of the RI, while for other transmission modes, CQI computation is based on RI=1. Subband CQI feedback for the mode 3-0 and the mode 3-1 is performed differentially. Modes 2-0 and 2-2 are for UE selected subband feedback. For the mode 2-0, a terminal side has to feed back a CQI for M preferred subbands and a wideband CQI. For transmission mode 3, different RIs have to be taken into account in CQI computation, while for a transmission mode other than the mode 3, RI=1 is assumed in CQI computation. For the mode 2-2, a terminal side has to feed back a PMI for M preferred subbands and a wideband PMI in addition to a CQI for M preferred subbands (computed based on a PMI for M preferred subbands) and a wideband CQI (computed based on a wideband PMI).
Periodic feedback is configured by a higher layer semi-statically, and may include modes as shown in Table 2.
TABLE 2PMI Feedback TypeNo PMISingle PMIPUCCH CQIWidebandMode 1-0Mode 1-1Feedback Type(wideband CQI)UE SelectedMode 2-0Mode 2-1(subband CQI)
For a transmission mode 9 and a terminal configured with 8 CSI-RS antenna ports, a mode 1-1 may include a sub-mode 1 and a sub-mode 2, configured via higher-layer signaling PUCCH_format_1-1_CSI_reporting_mode.
Different feedback periods and subframe biased feedback entities may be distinguished via periodic feedback types as follows.
Type 1 feedback reports a UE selected subband CQI.
Type 1a feedback includes a subband CQI and a second PMI.
Type 2, Type 2b and Type 2c feed back a wideband CQI and a PMI.
Type 2a feedback reports wideband PMI feedback.
Type 3 feedback reports an RI.
Type 4 feedback reports a wideband CQI.
Type 5 feedback reports an RI and a wideband PMI.
Type 6 feedback reports an RI and a PTI.
Wideband feedback includes a mode 1-0 and a mode 1-1. The mode 1-1 may further include a sub-mode 1 and a sub-mode 2. For the mode 1-0, a terminal side in transmission mode 3 feeds back a Type3 RI and a Type4 wideband CQI. For the mode 1-1, a Type3 RI and a wideband PMI and a wideband CQI of Type2 are fed back in a transmission mode other than the transmission mode 9 with 8 CSI-RS ports configured. For the sub-mode 1 of the mode 1-1 in the transmission mode 9 with 8 CSI-RS ports configured, a terminal side feeds back joint coding of the first wideband PMI and an RI of Type5 and joint coding of the second wideband PMI and a wideband CQI of Type2b. For the sub-mode 2 of the mode 1-1 in the transmission mode 9 with 8 CSI-RS ports configured, a terminal side feeds back joint coding of the second wideband PMI, the first wideband PMI and a wideband CQI of Type2c and a Type3 RI. A mode 2-0 and a mode 2-1 are for a UE selected subband CQI. For the mode 2-0, a terminal side in transmission mode 3 reports a Type3 RI, a Type4 wideband CQI and a Type1 intra-bandwidth subband CQI. For the transmission mode 2-1, in a transmission mode other than the transmission mode 9 with 8 CSI-RS ports configured, a Type1 intra-bandwidth subband CQI and joint coding of a PMI and a wideband CQI of Type2 and a Type3 RI may be fed back. For the mode 2-1 in the transmission mode 9 with 8 CSI-RS ports configured, joint coding of an RI and a PTI of Type6 is fed back, and then a way of feedback may further be selected according to the PTI. When PTI=0, a first wideband PMI of Type2a and then joint coding of the second wideband PMI and a wideband CQI of Type2b are fed back. When PTI=1, joint coding of the second wideband PMI and a wideband CQI of Type2b, and then joint coding of the second subband PMI and a subband CQI of 1a may be fed back.
Given that for R11 CoMP, a UE has to feed back CSI of multiple CSI-RS resources, the UE should feed back multiple sets of CSI in accordance with a certain feedback rule, regarding which, on one hand uplink feedback overheads have to be minimized, on the other hand feedback has to be performed in a way as simple and unified as possible, so as to reduce probability of a possible conflict in feedback information. However, at present, a CSI feedback rule is still in discussion, and no reference is provided by related art.